Method for incineration of combustible material in a continuous flow of a gaseous medium

ABSTRACT

A method and a fume incinerator apparatus for purifying a continuous flow of waste gas that contains combustible material by incinerating such material. The exemplary incinerator includes a chamber, a fuel-operated burner in the chamber, and flow control means for rapidly and thoroughly mixing waste gas and the hot gaseous products from the burner for highly effective and efficient incineration of the combustible material.

United States Patent Hirt 1451 Jan. 25, 1972 [54] METHOD FOR INCINERATION 0F 3,l64,445 1/1965 Hampel ..23/2 x COMBUSTIBLE MATERIAL IN A ggz zz A J i I n n v 1 s n v I l v v n s a s n 1 n I a I.

MEDIUM FOREIGN PATENTS OR APPLICATIONS [72] Inventor: John H. Hirt, Monterey Park, Calif. 691,894 8/1964 Canada ...23/2 [73] Assignee: l-lirt Combustion Engineers, Montebello, Primary Examiner Ear| c Thomas C ll Attorney-Miketta, Glenny, Poms and Smith F] d: A .26 1968 [22] pr 1571 ABSTRACT 2 348 App] No 7 A method and a fume incinerator apparatus for purifying a continuous flow of waste gas that contains combustible [52] U.S.Cl.....' ..23/2 C,23/277C material b incinerafing such material. The exemplary Cl 9/00 cinerator includes a chamber, a fuel-operated burner in the [58] Field of Search ..23/2, 2.1, 2 C, 277, 277 C chamber, and fl comm] means for rapidly and thoroughly mixing waste gas and the hot gaseous products from the [56] Ref n Cited burner for highly effective and efficient incineration of the b bl t l. UNITED STATES PATENTS e m em l,992,l36 2/1935 Wakefield ..23 2 Chimasnrawm! 8 r 3,090,675 5/1963 Rufi etal. f

PATENTED JANZSIQTE I 3.637.343 MEI 10? 3 INVENTOR.

Jo /v H. H/ET Y Whiz, I Amid MATERIAL IN A CONTINUOUS FLOW OF A GASEOUS MEDIUM BACKGROUND OF THE INVENTION In attempting to control air pollution, considerable attention has been directed to the control of combustible pollutant material contained in flue gases and other gaseous media that are discharged into the atmosphere incident, particularly, to various industrial operations and processes. For example, Los Angeles, California, presently requires a 90 percent reduction in the amount of total hydrocarbons, (normally measured in parts per millionp.p.m.) in a gas discharged into the atmosphere. To comply with this requirement, a gas containing 2,500 ppm. of total combustibles must be purified to a level of 250 p.p.m.

Various means have heretofore been tried for incinerating combustible material in such gas by burning added fuel to attempt to burn or incinerate combustible material before the gas is released to atmosphere. In general, such prior efforts have resulted in insufficient reduction in the amount of pollutants and/or have operated at low efficiency and high cost. Such a high percentage reduction is particularly difficult to achieve when the pollutants in the gas to be treated are already low, such as up to 1,000 p.p.m. (as methane equivalent).

It has generally been believed that the higher the temperature at which the pollutants are burned, the more effective will be the purification and that the polluted gas should therefore be introduced directly to the flame of the burner. Thus, governmental agencies entrusted with the enforcement of antiair pollution programs have usually required the incineration of these pollutants at or above certain specified temperatures. For example, it has been required that incineration be carried out at or above l,200 F. Accordingly, many prior incineration devices which burn a fuel to incinerate the combustibles in a flue gas have attempted to achieve high-temperature combustion by introducing the gas at or as close as possible to the location where the fuel is burned. This approach, however, does not make the most efficient use of the fuel because the flue gas lowers the temperature at which the fuel because the flue gas lowers the temperature at which the fuel is burned and thereby decreases its burning rate, which in turn increases the combustion volume requirements. The cost of fuel to operate such incinerators, particularly in large industrial installations, can be considerable, so that such a loss in effective combustion volume can reflect itself in high average operating temperatures which results in a substantial increase in cost of operating the incinerator as well as inefficiency in hydrocarbon reduction.

SUMMARY OF THE INVENTION The present invention contemplates first obtaining rapid, high-temperature (above 2,000 F.) combustion of fuel, and then mixing hot gaseous products from the burner and the flue gases for lower temperature incineration of the combustibles in the gas. The rapid, high-temperature combustion of the fuel affords higher efficient use of combustion space. Incineration at lower average temperatures offers obvious advantages such as fuel cost savings, reduction in insulation and maintenance required, and ability to use structural materials with a lower temperature tolerance.

It has been found that excellent results are achieved when certain flue gases are treated at lower temperatures, in the region of 900 to l,l F., rather than at higher temperatures of 1,200 F. or more, as previously thought necessary or at least desirable. These results appear to explain the low ignition temperature of many of the combustibles, i.e., in the order of normally between 800 and l,l00 F., which permits them to be incinerated at temperatures well below l,200 F. under optimum field operating conditions.

However, these lower temperatures can be used for effective and efficient incineration only if proper control is maintained over the operation. It is highly desirable that there be rapid and thorough mixing and circulation of the waste gas with the burner discharge to prevent any substantial portion of the gas from passing through the incinerator without being raised to a high enough temperature to incinerate the combustibles in such underheated portion of the gas.

It has also been found that the level of total combustibles in the waste gas may vary greatly for relatively small variations in temperature: very low levels of combustibles were achieved when the waste gas temperature was held within certain narrow temperature bands or ranges (e.g., T of about 40 to 50 or less) and high levels of combustibles were found at some relatively high waste gas temperatures. Thus, the rapid and thorough circulation and mixing of the waste gas is very important to bring temperature of as much as possible of the combustibles within such narrow ranges for the desired degree of incineration and for economical operation.

It will be noted that, while incineration at higher temperatures would theoretically permit substantial temperature variation without going below the ignition temperature of the combustibles, such higher temperature incineration not only involves high fuel cost and other associated disadvantages but may even result in high levels of combustibles.

It has also been found that very good results may be achieved when the retention time, i.e., the time period during which the waste gas is maintained at an elevated combustion" temperature, is reduced well below the time generally considered desirable for good incineration. One explanation for this surprising result is that the combustion of the pollutants in the gaseous medium is first achieved to a substantial degree in a very short time, e.g., less than 0.1 second, but that further reactions then take place which reverse this pattern, and produce increased amounts of combustible impurities which may again be subject to burning if sufficient time is then provided during cool down. This would explain the acceptable results achieved by longer retention times such as the 0.3 second or more currently required by the Los Angeles County, California, Pollution Control Authority.

A short retention time offers a number of advantages; principally, it permitsa shortening of the combustion chamber (decreased weight) at a substantial savings in initial cost support platform costs, installation, and in space requirements.

It has further been found that the introduction of a liquid water spray into the incoming flue gases facilitates removal of combustible material, particularly CO at lower operating temperatures.

Accordingly, the present invention contemplates efflciently and effectively incinerating combustibles in continuous flow of a gaseous medium by efficiently, rapidly burning added fuel and at a high temperature, and then mixing the hot gaseous products from such burning with the flow of the gaseous medium. The mixing should be rapid and thorough so as to raise the temperature of all the combustibles in the gaseous medium to the optimum temperature above the minimum combustion' temperature which will incinerate the combustibles and reduce the level of combustibles to below a determined acceptable value. Desirably, the combustibles are burned at relatively low temperatures within selected narrow ranges with high efficiency and effectiveness. Desirably also, the retention time may be made very short to minimize space requirements and cost.

It is an object of the present vinvention to provide a novel and improved methodand apparatus for economically, efficiently and effectively incinerating combustible particles in a continuous flow of a gaseous medium.

It is a further object of the invention to provide such apparatus which will effect rapid and thorough mixing and generally uniform temperature across the flow area of the gaseous medium through the apparatus.

It is another object of the present invention to achieve high efficiency, economical incineration of pollutants in a gaseous medium by employing a very short retention time and/or by introducing a liquid spray into the flue gas entering the incinerator.

it is another object of the present invention to achieve high efficiency, economical incineration of pollutants in a gaseous medium by careful and accurate temperature control to operate within a certain relatively low and narrow predetermined temperature band or range.

A specific object of the invention is to provide an incinerator apparatus having a ringlike shroud around a bumerblock for closely controlling and uniformly distributing air for the burner orifices.

Other objects and advantages of the present invention will become more apparent from the following description and the associated drawings.

IN THE DRAWINGS FIG. 1 is a vertical longitudinal section through a flue gas incinerator which is a presently preferred form of and embodies the present invention and which is operable in accordance with the method of the present invention.

FIGS. 2 and 3 are transverse sections taken generally along planes ll-ll AND llllll, respectively, of FIG. 1.

FIG. 4 is a graphic representation illustrating in general the amount of total combustibles in a flue gas passing through an incinerator as shown in FIGS. 1 to 3 at different temperatures of the gas.

FIG. 5 is a diagrammatic representation of the incinerator of FIGS. 1 to 3 and an associated graph illustrating. the variation in temperature measured transversely across the device at various points along its length.

FIG. 6 is a diagrammatic representation and associated graph similar to FIG. 5, but showing the entry baffle to the mixing chamber of the incinerator removed.

FIGS. 7 and 8 are diagrammatic representations from the side and end respectively, of a modified shorter form of fume incinerator.

Thev incinerator of the present invention is adapted to receive a continuous flow of gaseous medium such as waste or flue gas from an industrial operation and to rapidly and efficiently incinerate the combustible material in the gas to reduce the amount of such material to an acceptable predetermined value. The effluent gas is then discharged to the atmosphere, or into source device for removing heat, inorganic materials or both.

In general, an exemplary form of the incinerator, illustrated in FIGS. 1 to 3 and designated 10, includes an elongated chamber means 12 having an inlet 14 adjacent one end and an outlet 16 adjacent the other end. A fuel-operated burner means 18 is provided in chamber 12 adjacent to inlet 14. The burner means 18 receives a portion of the flow of flue gas from the inlet, using oxygen in the gas to burn an added fuel supply rapidly and at a relatively high temperature. The remainder or other portion of the flow of flue gas is mixed with the hot gaseous products discharged from the burner means as the combined flow moves toward outlet 16. The combined flow is rapidly and effectively mixed to achieve generally uniform temperature in flow area cross section and rapid incineration of the combustible material to reduce the amount of such material to a selected acceptable value. The purified flow is then discharged from outlet 16 of the incinerator to the atmosphere.

Incinerator in further detail, includes the chamber 12 which may conveniently be fabricated of a rear inlet or burner section 22 and a forward incineration, combustion or mixing section 24. The inlet section 22 and the mixing section 24 are each generally cylindrical and are shown coaxially connected together end-to-end to provide the elongated, horizontally extending tubular chamber means 12. if desired, the structure may be disposed at an inclined or in a vertical position.

The inlet section 22, which is closed at its rear end by a transversely extending wall 32, may be provided with suitable insulation such as by means of an inner lining of a refractory material. The inlet 14 of the illustrated incinerator 10 is provided by a transversely extending conduit connected to the inlet section 22 intermediate its ends and admitting gas to commence a symmetrical coaxial flow through the chamber means to provide uniformity of temperature and chemical properties across the chamber means. The inlet conduit 14 is adapted to connect to suitable conduits or pipes (not shown) which carry the continuous flow of flue gas to the incinerator.

A suitable means may be provided for introducing a spray of cool fluid such as water into the flow of gas entering the incinerator. in the illustrated incinerator 10, a spray nozzle 33 fed by a line 33a from a supply of water is provided at the wall of the inlet conduit 14.

The burner means 18 is supported generally coaxially within inlet section 22 and is mounted for selected positioning longitudinally of the section by suitable adjustable support means (not shown). Burner means 18 includes a rear air distribution wind box portion 34, a nozzle portion 39, and a forward combustion portion or tube 36. The portion 34, which may be of conventional construction, is connected to a suitable source of fuel, such as natural gas, by lines 38, 38a extending through the end wall 32. The portion 34 may include banks of burner nozzles 39 at its forward end and may have selectively variable intake means 40 at its rear end for controlling the amount of flue gas (whichcontains oxygen) taken into the burner nozzles for combustion of the fuel.

The burner combustion tube 36, which may be refractory lined, is mounted on the forward end of portion 34 and has a rear end wall 41 through which the burner nozzles 39 extend into the rear of the combustion tube 36. The burner combustion tube 36 extends forwardly into close proximity to a transverse ported wall 42 extending across the forward end of thechamber inlet section 22. The wall 42 may be of a portion of a rear end wall of chamber mixing section 24.

Combustion of the fuel rapidly and efficiently proceeds in the combustion tube 36 at relatively high temperatures, e.g., above 2,000" F., and the hot products of this combustion are discharged from the forward end of the tube 36.

The wall 42 is provided with a central port or opening 44 which is coaxially aligned with the forward or outlet end of the combustion tube 36. The port 44 is the same or less than the inner diameter of the burner combustion tube 36 for better mixing.

The flow of flue gas from the inlet conduit 14 is divided as it enters the chamber inlet section 22 as shown by arrows in FIG. 1. A portion of the flow passes rearwardly and then into the rear end of the burner through the intake means 40 to supply oxygen for combustion of the fuel in the burner and sometimes additional predilution of the products of combustion to aid in temperature uniformity. The other portion of the flow passes forwardly and then radially inwardly at the forward end of the burner to mix with the hot gaseous products discharged from the burner. The mixture then passes though the opening 44 into the mixing section 24.

The division of the flow of flue gas can be controlled by moving the burner means 18 forwardly and rearwardly to con trol the position of the forward end of the combustion tube 36 relative to the transverse wall 42. By restricting the flow area between the burner means and the wall 42, a greater portion of the flue gas flow will be caused to pass to the rear end of the burner means. Diameter of member 46 may be changed to effect restriction of flow.

Incinerator 10 may include an axial cylindrical member 46 at the forward end of the chamber inlet section 22 surrounding port 44. in the illustrated structure, cylindrical member 46 may be secured to the rear surface of the transverse wall 42 surrounding the port 44 and spaced radially inwardly from the inner surface of the chamber inlet section 22. Member 46 extends rearwardly so as to partially enclose or receive therein the forward end of burner combustion tube36. Member 46 may be supported and positioned by circumferentially spaced radially extending external ribs 46a. Member 46 affects radial gas distribution which facilitates initial mixing of the hot gaseous products from burner means 18 and the portion of the flow of flue gas that flows directly to the forward end of the burner means and can greatly affect pressure drop of the fume incinerator.

The chamber section 24 may be conveniently constructed of two parts, interconnected end-to-end as shown in FIG. 1 and lined with suitable refractory material. The mixing section 24 may have a larger inner diameter than that of the inlet section 22, except for its forward end portion which has a reduced diameter and provides the outlet 16 for the incinerator chamber. An annular shoulder 50 is thus formed at the rear end of section 24 surrounding the entrance to the outlet 16.

Suitable means may be provided for so diverting and directing the combined flow through the mixing section 24 as to effect circulation and mixing of the flow for substantial temperature uniformity transversely across the chamber: in general, the illustrated means include a first centrally disposed baffle means 52, an annular pucker ring 54, and the annular shoulder 50 surrounding the outlet 16. The spacing between inlet orifice 44 and baffle 52 and between baffle 52 and pucker ring 54 may be approximately equal and as short as possible commensurate with acceptable pressure drop. Likewise the smaller the orifices and the larger the pucker ring, the better the mixing and the greater the pressure drop.

More particularly, the flow of combined gas from the port 44 is first mixed and diverted radially outwardly. This is achieved by the first baffle means 52 which extends transversely of the mixing section 24 a short distance forward or downstream from port 44 to block the central portion of the chamber 24. The combined flow through the port 44 cascades or splatters against the opposed surface of baffle means 52, causing substantial agitation and mixing of the flow. The flow then continues forwardly around the annular edges of the baffle means 52 toward the outlet end of the incinerator. The illustrated baffle means 52 is in the form of a circular plate of refractory material supported coaxially within the mixing section 24 as by means of circumferentially spaced brick feet 58 (FIG. 3). The flow area around baffle means 52 and between the feet 58 is desirably sufficient so as to meet allowable pressure drop parameters through the incinerator.

The flow is next diverted radially inwardly to provide furthermixing. This is provided in the illustrated incinerator by the annular pucker ring means 54 which is spaced forwardly or downstream from first baffle means 52 and which extends inwardly from the sidewall 23 of the mixing section 24. The pucker ring means 54 may be constructed of suitable refractory material and secured to the sidewall.

After the flow is permitted to expand downstream of the pucker ring 54, it is again diverted radially inwardly by annular shoulder 50 surrounding the outlet 16 and permitted to flow out of the incinerator through the outlet 16.

The flow from the outlet 16 may be immediately cooled as by means of the introduction of cool air to a fan 60 positioned at the exit of the outlet to facilitate cooling the gases so that fan 60 may be constructed of lower operating temperature materials. When a forced shaft incinerator is used, the gases may be conducted in a refractory lined duct to atmosphere or diluted with colder air so they may be conducted to atmosphere by a duct made of lower temperature materials. The flow may then be exhausted to the atmosphere.

The graph of FIG. 4 indicates that the amount of combustible material in the gaseous medium is reduced to a low level when the temperature of all the gaseous medium is in certain narrow ranges, and that the level may become higher when the temperature is between the temperatures of these ranges.

By keeping the gas temperature in one of these ranges, a high proportion of the combustible material in the gas may be incinerated. For economy of fuel cost, it is of course desirable to operate in the lowest of these temperature ranges which will give satisfactory incineration of the combustibles in the gas.

In prior incinerator constructions H6. 6 illustrates that without the first baffle means in the incinerator construction, while the temperature variation in transverse sections of the flowing gas is substantially reduced by the time the gas is discharged through the outlet, the variations are in general too large to maintain the temperature of substantially all of the gas flow within one of the selected narrow temperature ranges for a long enough time to insure the desired degree of incineration of the combustibles thereby requiring the raising of average temperature of operation of the incinerator so as to bring the minimum gas temperature above the destruction temperatures.

FIG. 5 illustrates that with the addition of the first baffle means to the incinerator construction, the temperature differential across sections of the chamber 24 is rapidly reduced in moving forwardly along the chamber 24 so that virtually all of the flue gas can be brought within the selected range to insure the desired degree of incineration of the combustibles in the gas. 4

Thus, the incinerator 10 is simple and economical to build, install and maintain. It makes efficient of fuel by permitting the fuel to be burned at relatively high temperatures and using 0 from the flue gas for combustion when available (no premix burner). The hot products of that combustion are rapidly and well mixed with the flue gas or the like, for effective incineration of the combustibles in the flue gas. The combustibles may be incinerated at relatively low temperatures by providing thorough mixing so that virtually all of the combustibles will be brought to temperatures above their ignition temperatures for substantial complete incineration or destruction.

FIGS. 7 and 8 illustrate a modified form of apparatus 10a in which the chamber mixing section 24a has been greatly shortened and the pucker ring 54 has been in effect removed. This shortened chamber 12a operates on a much shorter retention time than does the chamber 12, typical values being on the order of about 0.] seconds or less for chamber 12a to 0.3 seconds for chamber 12. As noted above, it is believed that, at least for some situations, following an initial oxidation (e.g., 0.1 seconds), there are further regressive reactions due to added time (e.g., to 0.3 seconds) which reduces the degree of oxidation and which may increase the reversal of some of the oxidation products, that is, CO CO. Thus, it is believed that rapid mixing and heating of the flue gas followed by quick cool down to stop further regressive reactions in the gas may be the reason for the good results achieved by the shortened apparatus 10a. This reduction in length and material produces direct cost, space and temperature savings and provides a more flexible, convenient unit.

Various other modifications and changes may be made in the illustrated structure and in the method of its operation without departing from the spirit and scope of the invention.

lclaim:

1. In a method for incinerating combustible material in a continuous flow of a gaseous medium, said method comprising the steps of:

a. continuously directing flow of the combustion products of a burning fuel into a path having a flow area at least not greater than the burning area of the burning fuel;

b. introducing a gaseous medium containing combustible material into said flow of combustion products upstream of said path;

c. directing and discharging said combustion products and gaseous medium into a first space of enlarged cross-sectional area with respect to the flow area of said path;

(1. centrally obstructing the flow of the discharged combustion products and gaseous medium downstream of said path for thorough mixing thereof in said first space;

e. and directing said mixed combustion products and medi um out of said first space by passing said mixture through flow areas radially outwardly located with respect to said path and into a second space of enlarged cross-sectional area; whereby the temperature of said combustible material in said gaseous medium is raised to at least its ignition temperature and a generally uniform temperature across the flow cross-sectional area of said mixture in said spaces is achieved.

2. A method as stated in claim 1 including the steps of: raising the temperature of virtually all of the combustible material to at least its ignition temperature within 0.1

second, and

900 F. and below about l,400 F. 5. In the method as stated in claim 1 including the step of: diverting part of the gaseous medium containing combustible material to the'burning fuel supplying additional oxygen for burning of fuel. 6. In a method as stated in claim 1 including the step of: diverting the flow of said mixture in said second space radially inwardly of said radially outwardly located flow areas to cause further mixing within said second space. 

2. A method as stated in claim 1 including the steps of: raising the temperature of virtually all of the combustible material to at least its ignition temperature within 0.1 second, and rapidly cooling the mixture to a nonreactive temperature.
 3. A method as stated in claim 1 including the step of: raising virtually all incremental areas in a flow cross-sectional area of the mixture in said spaces to uniform temperatures in the range of from about 950* to about 1,350* F.
 4. A method as defined in claim 1 including the steps: burning said gaseous fuel at a temperature above about 2,000* F., and maintaining said mixture in a selected cross-sectional flow area in a uniform temperature range above about 900* F. and below about 1,400* F.
 5. In the method as stated in claim 1 including the step of: diverting part of the gaseous medium containing combustible material to the burning fuel supplying additional oxygen for burning of fuel.
 6. In a method as stated in claim 1 including the step of: diverting the flow of said mixture in said second space radially inwardly of said radially outwardly located flow areas to cause further mixing within said second space. 